Liquid product is commonly delivered to a customer and the amount of liquid product is often measured by a liquid flow meter as the product is pumped from a supply tank or truck tank to the customer's storage tank. The accuracy of such liquid flow meters is often controlled by state and/or federal regulations. As the supply tank used to transport the liquid product becomes empty, a mixture of air and liquid can be pumped by the delivery pump and through the liquid flow meter to the customer's storage tank. This mixture of air and liquid through the flow meter causes the flow meter to inaccurately measure the amount of liquid product delivered as both air volume and liquid volume are measured by conventional flow meters. Thus, it is often necessary to remove or separate the air from the liquid during the delivery process in order to accurately measure the amount of liquid delivered.
This problem is particularly prevalent when petroleum products are delivered to a customer's storage tank using a delivery truck. To ensure that the customer gets the amount of liquid product paid for, a so-called “split compartment” test or product depletion test is carried out. A compartment of the delivery truck (i.e., supply tank) must be drained completely during the delivery process causing the truck's pump to suck air and liquid into the metering line. To pass this test, the air must be exhausted before the air can be pumped through the liquid flow meter with the liquid and out the delivery hose. By sensing the air/liquid mixture and eliminating the air, one prevents an over registration of the actual liquid product delivered.
Therefore, air separation systems have been developed to address this problem. Traditional air separation systems rely upon a float system with an additional level-sensing chamber disposed above the chamber that includes a strainer that is in-line upstream of the liquid flow meter. The level-sensing chamber typically houses the float. When the float drops below a predetermined level, the system actuates a mechanical valve that releases air from the level-sensing chamber upstream of the liquid flow meter. Such systems may also shut off flow to the liquid flow meter until the float rises above the predetermined level indicating that the chamber includes a sufficient amount of liquid so that metering can recommence.
The disadvantages of these systems include leaks in the float, wear and tear of the float and valve mechanism, valve seal degradation and other various leakage problems.
More recently, electronic sensors have been employed with electrically actuated valves. However, these systems utilize in-line sensing devices such as dielectric constant sensors or density sensing probes. These sensors are expensive, require sophisticated electronics and require frequent calibration that result in higher costs than the previously used mechanical air separators.
Therefore, there is a need for an improved air separation system which is economical to manufacture and which requires only infrequent servicing or maintenance.